1. Field of the Invention
The present invention relates to technology for controlling the fuel pressure supplied to fuel injection valves of an engine.
2. Related Art of the Invention
As a fuel supply device to an engine, there has been proposed a system of a constitution in which, in order to prevent a rise in the fuel temperature due to excess fuel returned from a pressure regulator to a fuel tank, the pressure regulator is abolished but, instead, a sensor is provided to detect the fuel pressure in a fuel supply passage, and the discharge amount of the fuel pump is controlled according to the fuel pressure detected by the sensor in order to obtain the fuel pressure required by the operation conditions, so that the discharge amount of the fuel pump is made to correspond to a required fuel amount, to suppress the generation of excess fuel (see Japanese Unexamined Patent Publication No. 7-293397).
In the fuel supply device of this type, the fuel pressure is required to be as low as possible in order to reduce the electric power consumption of the fuel pump. In order to prevent the fuel from vaporizing in the fuel supply passage under a heat-resisting environmental condition (high temperature condition), however, a margin has been imparted to the lower limit value of a target fuel pressure; i.e., the lower limit value of the target fuel pressure has been set to be slightly high. Accordingly, the fuel pressure is not lowered to a sufficient degree, and the consumption of electric power is not saved to a sufficient degree.
There has also been proposed a technology for setting the lower limit value of the fuel pressure so that the fuel is injected in a required amount within a limited fuel injection period at the start of engine. This, however, is not to lower the fuel pressure (see Japanese Unexamined Patent Publication No. 9-222037).
The present invention was accomplished in view of the above-mentioned conventional problem, and its object is to accomplish a sufficient effect by reduction of electrical power consumption by controlling the fuel pressure to a minimum required level.
It is a further object of the present invention to accomplish the above-mentioned effect with a simple constitution.
It is a further object of the present invention to maintain the above-mentioned effect to a sufficient degree by controlling the fuel pressure with a high accurately.
In order to accomplish the above-mentioned objects, according to the present invention, the constitution is such that an operation of a fuel pump is controlled so that the pressure of fuel supplied from the fuel pump to a fuel injection valve becomes a target fuel pressure corresponding to an engine operation condition, and a lower limit value of the target fuel pressure is set according to an engine environmental temperature.
In this way, during the engine operation, the fuel pressure is controlled to become the target fuel pressure set corresponding to the engine operation condition. Here, the engine environmental temperature participating with the fuel vapor generation is detected, and the lower limit value of the target fuel pressure is variably set according to the engine environmental temperature.
With this constitution, under the condition of low engine environmental temperature, the lower limit value is set to be low, so that the target fuel pressure is prevented from being limited to a higher value by the lower limit value and, hence, reducing the electric power consumption of the fuel pump to a sufficient degree and enhancing the fuel economy.
The constitution may be such that an engine cooling water temperature is detected and, hence, an engine environmental temperature condition is detected based on the detected value.
With this constitution, the engine environmental temperature condition participating with the fuel vapor generation is easily detected without the rise of cost, since a value detected by a water temperature sensor indispensable the engine control is used.
Further, the constitution may be such that an outer air temperature is detected in addition to the engine cooling water temperature and, hence, the engine environmental temperature condition is detected based on these detected values.
With this constitution, by using the outer air temperature as well as the engine cooling water temperature, it is possible to more accurately detect the engine environmental temperature condition participating with the fuel vapor generation.
Further, the constitution may be such that an on or off state of an air conditioner is detected in addition to the engine cooling water temperature and, hence, the engine environmental temperature condition is detected based on these detected values.
With this constitution, by adding the on or off information of the air conditioner switch as well as the engine cooling water temperature, it is possible to more accurately detect the engine environmental temperature condition participating with the fuel vapor generation.
Moreover, the constitution may be such that the fuel temperature is detected and, hence, the engine environmental temperature is detected based on the detected value.
With this constitution, by using the fuel temperature directly detected, it is possible to most accurately detect the engine environmental temperature condition participating with the fuel vapor generation.
Furthermore, the constitution may be such that the fuel pressure is detected to feedback control the fuel pressure to the target fuel pressure based on the detected value.
That is, a high accurate control becomes possible by adapting the present invention to a feedback control system, although the present invention can also be adapted to a feedforward control system.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.